MPLS Working Group B. Niven-Jenkins, Ed.
Internet-Draft BT
Intended status: Standards Track D. Brungard, Ed.
Expires: February 17, 2010 AT&T
M. Betts, Ed.
Huawei Technologies
N. Sprecher
Nokia Siemens Networks
S. Ueno
NTT
August 16, 2009
MPLS-TP Requirementsdraft-ietf-mpls-tp-requirements-10
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and restrictions with respect to this document.
Abstract
This document specifies the requirements of an MPLS Transport Profile
(MPLS-TP). This document is a product of a joint International
Telecommunications Union (ITU)-IETF effort to include an MPLS
Transport Profile within the IETF MPLS and PWE3 architectures to
support the capabilities and functionalities of a packet transport
network as defined by International Telecommunications Union -
Telecommunications Standardization Sector (ITU-T).
This work is based on two sources of requirements; MPLS and PWE3
architectures as defined by IETF, and packet transport networks as
defined by ITU-T.
The requirements expressed in this document are for the behavior of
the protocol mechanisms and procedures that constitute building
blocks out of which the MPLS transport profile is constructed. The
requirements are not implementation requirements.
Requirements Language
Although this document is not a protocol specification, the key words
"MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD",
"SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" are to be
interpreted as described in RFC 2119 [RFC2119] and are to be
interpreted as instructions to the protocol designers producing
solutions that satisfy the requirements set out in this document.
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Internet-Draft MPLS-TP Requirements August 20091. Introduction
Bandwidth demand continues to grow worldwide, stimulated by the
accelerating growth and penetration of new packet based services and
multimedia applications:
o Packet-based services such as Ethernet, Voice over IP (VoIP),
Layer 2 (L2)/Layer 3 (L3) Virtual Private Networks (VPNs), IP
Television (IPTV), Radio Access Network (RAN) backhauling, etc.,
o Applications with various bandwidth and Quality of Service (QoS)
requirements.
This growth in demand has resulted in dramatic increases in access
rates that are, in turn, driving dramatic increases in metro and core
network bandwidth requirements.
Over the past two decades, the evolving optical transport
infrastructure (Synchronous Optical Networking (SONET)/Synchronous
Digital Hierarchy (SDH), Optical Transport Network (OTN)) has
provided carriers with a high benchmark for reliability and
operational simplicity.
With the movement towards packet based services, the transport
network has to evolve to encompass the provision of packet aware
capabilities while enabling carriers to leverage their installed, as
well as planned, transport infrastructure investments.
Carriers are in need of technologies capable of efficiently
supporting packet based services and applications on their transport
networks with guaranteed Service Level Agreements (SLAs). The need
to increase their revenue while remaining competitive forces
operators to look for the lowest network Total Cost of Ownership
(TCO). Investment in equipment and facilities (Capital Expenditure
(CAPEX)) and Operational Expenditure (OPEX) should be minimized.
There are a number of technology options for carriers to meet the
challenge of increased service sophistication and transport
efficiency, with increasing usage of hybrid packet transport and
circuit transport technology solutions. To realize these goals, it
is essential that packet transport technology be available that can
support the same high benchmarks for reliability and operational
simplicity set by SDH/SONET and OTN technologies.
Furthermore for carriers it is important that operation of such
packet transport networks should preserve the look-and-feel to which
carriers have become accustomed in deploying their optical transport
networks, while providing common, multi-layer operations, resiliency,
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control and multi-technology management.
Transport carriers require control and deterministic usage of network
resources. They need end-to-end control to engineer network paths
and to efficiently utilize network resources. They require
capabilities to support static (management plane based) or dynamic
(control plane based) provisioning of deterministic, protected and
secured services and their associated resources.
It is also important to ensure smooth interworking of the packet
transport network with other existing/legacy packet networks, and
provide mappings to enable packet transport carriage over a variety
of transport network infrastructures. The latter has been termed
vertical interworking, and is also known as client/server or network
interworking. The former has been termed horizontal interworking,
and is also known as peer-partition or service interworking. For
more details on interworking and some of the issues that may arise
(especially with horizontal interworking) see G.805 [ITU.G805.2000]
and Y.1401 [ITU.Y1401.2008].
Multi-Protocol Label Switching (MPLS) is a maturing packet technology
and it is already playing an important role in transport networks and
services. However, not all of MPLS's capabilities and mechanisms are
needed and/or consistent with transport network operations. There
are also transport technology characteristics that are not currently
reflected in MPLS. There is therefore the need to define an MPLS
Transport Profile (MPLS-TP) that supports the capabilities and
functionalities needed for packet transport network services and
operations through combining the packet experience of MPLS with the
operational experience and practices of existing transport networks.
MPLS-TP will enable the deployment of packet based transport networks
that will efficiently scale to support packet services in a simple
and cost effective way. MPLS-TP needs to combine the necessary
existing capabilities of MPLS with additional minimal mechanisms in
order that it can be used in a transport role.
This document specifies the requirements of an MPLS Transport Profile
(MPLS-TP). The requirements are for the behavior of the protocol
mechanisms and procedures that constitute building blocks out of
which the MPLS transport profile is constructed. That is, the
requirements indicate what features are to be available in the MPLS
toolkit for use by MPLS-TP. The requirements in this document do not
describe what functions an MPLS-TP implementation supports. The
purpose of this document is to identify the toolkit and any new
protocol work that is required.
This document is a product of a joint ITU-T and IETF effort to
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include an MPLS Transport Profile within the IETF MPLS and PWE3
architectures to support the capabilities and functionalities of a
packet transport network as defined by ITU-T. The document is a
requirements specification, but is presented on the Standards Track
so that it can be more easily cited as a normative reference from
within the work of the ITU-T.
This work is based on two sources of requirements, MPLS and PWE3
architectures as defined by IETF and packet transport networks as
defined by ITU-T. The requirements of MPLS-TP are provided below.
The relevant functions of MPLS and PWE3 are included in MPLS-TP,
except where explicitly excluded. Any new functionality that is
defined to fulfill the requirements for MPLS-TP must be agreed within
the IETF through the IETF consensus process as per [RFC4929].
MPLS-TP transport paths may be established using static or dynamic
configuration. It should be noted that the MPLS-TP network and its
transport paths can always be operated fully (including OAM and
protection capabilities) in the absence of any control plane.
1.1. Terminology
Note: Mapping between the terms in this section and ITU-T terminology
is described in [I-D.helvoort-mpls-tp-rosetta-stone].
The recovery requirements in this document use the recovery
terminology defined in RFC 4427 [RFC4427], this is applied to both
control plane and management plane based operations of MPLS-TP
transport paths.
1.1.1. Abbreviations
ASON: Automatically Switched Optical Network
ATM: Asynchronous Transfer Mode
CAPEX: Capital Expenditure
CE: Customer Edge
FR: Frame Relay
GMPLS: Generalised Multi-Protocol Label Switching
IGP: Interior Gateway Protocol
IPTV: IP Television
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VPN: Virtual Private Network
WDM: Wavelength Division Multiplexing
1.1.2. Definitions
Note: The definition of segment in a GMPLS/ASON context (i.e. as
defined in RFC4397 [RFC4397]) encompasses both segment and
concatenated segment as defined in this document.
Associated bidirectional path: A path that supports traffic flow in
both directions but which is constructed from a pair of
unidirectional paths (one for each direction) which are associated
with one another at the path's ingress/egress points. The forward
and backward directions are setup, monitored and protected
independently. As a consequence they may or may not follow the same
route (links and nodes) across the network.
Client layer network: In a client/server relationship (see G.805
[ITU.G805.2000]), the client layer network receives a (transport)
service from the lower server layer network (usually the layer
network under consideration).
Concatenated Segment: A serial-compound link connection as defined in
G.805 [ITU.G805.2000]. A concatenated segment is a contiguous part
of an LSP or multi-segment PW that comprises a set of segments and
their interconnecting nodes in sequence. See also "Segment".
Control Plane: Within the scope of this document the control plane
performs transport path control functions. Through signalling, the
control plane sets up, modifies and releases transport paths, and may
recover a transport path in case of a failure. The control plane
also performs other functions in support of transport path control,
such as routing information dissemination.
Co-routed Bidirectional path: A path where the forward and backward
directions follow the same route (links and nodes) across the
network. Both directions are setup, monitored and protected as a
single entity. A transport network path is typically co-routed.
Domain: A domain represents a collection of entities (for example
network elements) that are grouped for a particular purpose, examples
of which are administrative and/or managerial responsibilities, trust
relationships, addressing schemes, infrastructure capabilities,
aggregation, survivability techniques, distributions of control
functionality, etc. Examples of such domains include IGP areas and
Autonomous Systems.
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Layer network: Layer network is defined in G.805 [ITU.G805.2000]. A
layer network provides for the transfer of client information and
independent operation of the client OAM. A Layer Network may be
described in a service context as follows: one layer network may
provide a (transport) service to higher client layer network and may,
in turn, be a client to a lower layer network. A layer network is a
logical construction somewhat independent of arrangement or
composition of physical network elements. A particular physical
network element may topologically belong to more than one layer
network, depending on the actions it takes on the encapsulation
associated with the logical layers (e.g. the label stack), and thus
could be modeled as multiple logical elements. A layer network may
consist of one or more sublayers. Section 1.3 provides a more
detailed overview of what constitutes a layer network. For
additional explanation of how layer networks relate to the OSI
concept of layering see Appendix I of Y.2611 [ITU.Y2611.2006].
Link: A physical or logical connection between a pair of LSRs that
are adjacent at the (sub)layer network under consideration. A link
may carry zero, one or more LSPs or PWs. A packet entering a link
will emerge with the same label stack entry values.
MPLS-TP Logical Ring: An MPLS-TP logical ring is constructed from a
set of LSRs and logical data links (such as MPLS-TP LSP tunnels or
MPLS-TP pseudowires) and physical data links that form a ring
topology.
Path: See Transport Path.
MPLS-TP Physical Ring: An MPLS-TP physical ring is constructed from a
set of LSRs and physical data links that form a ring topology.
MPLS-TP Ring Topology: In an MPLS-TP ring topology each LSR is
connected to exactly two other LSRs, each via a single point-to-point
bidirectional MPLS-TP capable link. A ring may also be constructed
from only two LSRs where there are also exactly two links. Rings may
be connected to other LSRs to form a larger network. Traffic
originating or terminating outside the ring may be carried over the
ring. Client network nodes (such as CEs) may be connected directly
to an LSR in the ring.
Section Layer Network: A section layer is a server layer (which may
be MPLS-TP or a different technology) which provides for the transfer
of the section layer client information between adjacent nodes in the
transport path layer or transport service layer. A section layer may
provide for aggregation of multiple MPLS-TP clients. Note that G.805
[ITU.G805.2000] defines the section layer as one of the two layer
networks in a transmission media layer network. The other layer
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network is the physical media layer network.
Segment: A link connection as defined in G.805 [ITU.G805.2000]. A
segment is the part of an LSP that traverses a single link or the
part of a PW that traverses a single link (i.e. that connects a pair
of adjacent {Switching|Terminating} Provider Edges). See also
"Concatenated Segment".
Server Layer Network: In a client/server relationship (see G.805
[ITU.G805.2000]), the server layer network provides a (transport)
service to the higher client layer network (usually the layer network
under consideration).
Sublayer: Sublayer is defined in G.805 [ITU.G805.2000]. The
distinction between a layer network and a sublayer is that a sublayer
is not directly accessible to clients outside of its encapsulating
layer network and offers no direct transport service for a higher
layer (client) network.
Switching Provider Edge (S-PE): See [I-D.ietf-pwe3-ms-pw-arch].
Terminating Provider Edge (T-PE): See [I-D.ietf-pwe3-ms-pw-arch].
Transport Path: A network connection as defined in G.805
[ITU.G805.2000]. In an MPLS-TP environment a transport path
corresponds to an LSP or a PW.
Transport Path Layer: A (sub-)layer network that provides point-to-
point or point-to-multipoint transport paths. It provides
independent (of the client) OAM when transporting its clients.
Transport Service Layer: A layer network in which transport paths are
used to carry a customer's (individual or bundled) service (may be
point-to-point, point-to-multipoint or multipoint-to-multipoint
services).
Transmission Media Layer: A layer network, consisting of a section
layer network and a physical layer network as defined in G.805
[ITU.G805.2000], that provides sections (two-port point-to-point
connections) to carry the aggregate of network transport path or
network service layers on various physical media.
Unidirectional Path: A path that supports traffic flow in only one
direction.
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Internet-Draft MPLS-TP Requirements August 20091.2. Transport network overview
The connectivity service is the basic service provided by a transport
network. The purpose of a transport network is to carry its customer
traffic (i.e. the stream of customer PDUs or customer bits, including
overhead) between endpoints in the transport network (typically over
several intermediate nodes). The connectivity services offered to
customers are typically aggregated into large transport paths with
long-holding times and independent OAM (of the client OAM), which
contribute to enabling the efficient and reliable operation of the
transport network. These transport paths are modified infrequently.
Quality-of-service mechanisms are required in the packet transport
network to ensure the prioritization of critical services, to
guarantee bandwidth and to control jitter and delay. A transport
network must provide the means to commit quality of service
objectives to clients. This is achieved by providing a mechanism for
client network service demarcation for the network path together with
an associated network resiliency mechanism.
Aggregation is beneficial for achieving scalability and security
since:
1. It reduces the number of provisioning and forwarding states in
the network core.
2. It reduces load and the cost of implementing service assurance
and fault management.
3. Customer traffic is encapsulated and layer associated OAM
overhead is added. This allows complete isolation of customer
traffic and its management from carrier operations.
An important attribute of a transport network is that it is able to
function regardless of which clients are using its connection service
or over which transmission media it is running. The client,
transport network and server layers are from a functional and
operations point of view independent layer networks. Another key
characteristic of transport networks is the capability to maintain
the integrity of the client across the transport network. A
transport network must also provide a method of service monitoring in
order to verify the delivery of an agreed quality of service. This
is enabled by means of carrier-grade OAM tools.
Customer traffic is first encapsulated within the transport service
layer network. The transport service layer network signals may then
be aggregated into a transport path layer network for transport
through the network in order to optimize network management.
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Transport service layer network OAM is used to monitor the transport
integrity of the customer traffic and transport path layer network
OAM is used to monitor the transport integrity of the aggregates. At
any hop, the aggregated signals may be further aggregated in lower
layer transport network paths for transport across intermediate
shared links. The transport service layer network signals are
extracted at the edges of aggregation domains, and are either
delivered to the customer or forwarded to another domain. In the
core of the network, only the transport path layer network signals
are monitored at intermediate points; individual transport service
layer network signals are monitored at the network boundary.
Although the connectivity of the transport service layer network may
be point-to-point, point-to-multipoint or multipoint-to-multipoint,
the transport path layer network only provides point-to-point or
point-to-multipoint transport paths which are used to carry
aggregates of transport service layer network traffic.
1.3. Layer network overview
A layer network provides its clients with a transport service and the
operation of the layer network is independent of whatever client
happens to use the layer network. Information that passes between
any client to the layer network is common to all clients and is the
minimum needed to be consistent with the definition of the transport
service offered. The client layer network can be connectionless,
connection oriented packet switched, or circuit switched. The
transport service transfers a payload (individual packet payload for
connectionless networks, a sequence of packets payloads in the case
of connection oriented packet switched networks, and a deterministic
schedule of payloads in the case of circuit switched networks) such
that the client can populate the payload without affecting any
operation within the serving layer network.
The operations within a layer network that are independent of its
clients include the control of forwarding, the control of resource
reservation, the control of traffic demerging, and the OAM and
recovery of the transport service. All of these operations are
internal to a layer network. By definition, a layer network does not
rely on any client information to perform these operations and
therefore all information required to perform these operations is
independent of whatever client is using the layer network.
A layer network will have consistent features in order to support the
control of forwarding, resource reservation, OAM and recovery. For
example, a layer network will have a common addressing scheme for the
end points of the transport service and a common set of transport
descriptors for the transport service. However, a client may use a
different addressing scheme or different traffic descriptors
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(consistent with performance inheritance).
It is sometimes useful to independently monitor a smaller domain
within a layer network (or the transport services that traverse this
smaller domain) but the control of forwarding or the control of
resource reservation involved retain their common elements. These
smaller monitored domains are sublayers.
It is sometimes useful to independently control forwarding in a
smaller domain within a layer network but the control of resource
reservation and OAM retain their common elements. These smaller
domains are partitions of the layer network.
2. MPLS-TP Requirements
The MPLS-TP requirements set out in this section are for the behavior
of the protocol mechanisms and procedures that constitute building
blocks out of which the MPLS transport profile is constructed. That
is, the requirements indicate what features are to be available in
the MPLS toolkit for use by MPLS-TP.
2.1. General requirements
1 The MPLS-TP data plane MUST be a subset of the MPLS data plane as
defined by the IETF. When MPLS offers multiple options in this
respect, MPLS-TP SHOULD select the minimum sub-set (necessary and
sufficient subset) applicable to a transport network application.
2 The MPLS-TP design SHOULD as far as reasonably possible re-use
existing MPLS standards.
3 Mechanisms and capabilities MUST be able to interoperate with
existing IETF MPLS [RFC3031] and IETF PWE3 [RFC3985] control and
data planes where appropriate.
A. Data plane interoperability MUST NOT require a gateway
function.
4 MPLS-TP and its interfaces, both internal and external, MUST be
sufficiently well-defined that interworking equipment supplied by
multiple vendors will be possible both within a single domain,
and between domains.
5 MPLS-TP MUST be a connection-oriented packet switching technology
with traffic engineering capabilities that allow deterministic
control of the use of network resources.
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6 MPLS-TP MUST support traffic engineered point to point (P2P) and
point to multipoint (P2MP) transport paths.
7 MPLS-TP MUST support unidirectional, co-routed bidirectional and
associated bidirectional point-to-point transport paths.
8 MPLS-TP MUST support unidirectional point-to-multipoint transport
paths.
9 The end points of a co-routed bidirectional transport path MUST
be aware of the pairing relationship of the forward and reverse
paths used to support the bidirectional service.
10 All nodes on the path of a co-routed bidirectional transport path
in the same (sub-)layer as the path MUST be aware of the pairing
relationship of the forward and the backward directions of the
transport path.
11 The end points of an associated bidirectional transport path MUST
be aware of the pairing relationship of the forward and reverse
paths used to support the bidirectional service.
12 Nodes on the path of an associated bidirectional transport path
where both the forward and backward directions transit the same
node in the same (sub-)layer as the path SHOULD be aware of the
pairing relationship of the forward and the backward directions
of the transport path.
13 MPLS-TP MUST support bidirectional transport paths with symmetric
bandwidth requirements, i.e. the amount of reserved bandwidth is
the same between the forward and backward directions.
14 MPLS-TP MUST support bidirectional transport paths with
asymmetric bandwidth requirements, i.e. the amount of reserved
bandwidth differs between the forward and backward directions.
15 MPLS-TP MUST support the logical separation of the control and
management planes from the data plane.
16 MPLS-TP MUST support the physical separation of the control and
management planes from the data plane. That is, it must be
possible to operate the control and management planes out-of-band
and no assumptions should be made about the state of the data
plane channels from information about the control or management
plane channels when they are running out-of-band.
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17 MPLS-TP MUST support static provisioning of transport paths via
the management plane.
18 A solution MUST be defined to support dynamic provisioning and
restoration of MPLS-TP transport paths via a control plane.
19 Static provisioning MUST NOT depend on the presence of any
element of a control plane.
20 MPLS-TP MUST support the co-existence of statically and
dynamically provisioned/managed MPLS-TP transport paths within
the same layer network or domain.
21 Mechanisms in an MPLS-TP layer network that satisfy functional
requirements that are common to general transport layer networks
(i.e., independent of technology) SHOULD be operable in a way
that is similar to the way the equivalent mechanisms are operated
in other transport layer technologies.
22 MPLS-TP MUST support the capability for network operation via the
management plane (without the use of any control plane
protocols). This includes the configuration and control of OAM
and recovery functions.
23 The MPLS-TP data plane MUST be capable of
A. forwarding data independent of the control or management
plane used to configure and operate the MPLS-TP layer
network.
B. taking recovery actions independent of the control or
management plane used to configure the MPLS-TP layer network.
C. operating normally (i.e. forwarding, OAM and protection MUST
continue to operate) if the management plane or control plane
that configured the transport paths fails.
24 MPLS-TP MUST support mechanisms to avoid or minimize traffic
impact (e.g. packet delay, reordering and loss) during network
reconfiguration.
25 MPLS-TP MUST support transport paths through multiple homogeneous
domains.
26 MPLS-TP SHOULD support transport paths through multiple non-
homogeneous domains.
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27 MPLS-TP MUST NOT dictate the deployment of any particular network
topology either physical or logical, however:
A. It MUST be possible to deploy MPLS-TP in rings.
B. It MUST be possible to deploy MPLS-TP in arbitrarily
interconnected rings with one or two points of
interconnection.
C. MPLS-TP MUST support rings of at least 16 nodes in order to
support the upgrade of existing TDM rings to MPLS-TP.
MPLS-TP SHOULD support rings with more than 16 nodes.
28 MPLS-TP MUST be able to scale at least as well as existing
transport technologies with growing and increasingly complex
network topologies as well as with increasing bandwidth demands,
number of customers, and number of services.
29 MPLS-TP SHOULD support mechanisms to safeguard against the
provisioning of transport paths which contain forwarding loops.
2.2. Layering requirements
30 A generic and extensible solution MUST be provided to support the
transport of one or more client layer networks (e.g. MPLS-TP,
IP, MPLS, Ethernet, ATM, FR, etc.) over an MPLS-TP layer network.
31 A generic and extensible solution MUST be provided to support the
transport of MPLS-TP transport paths over one or more server
layer networks (such as MPLS-TP, Ethernet, SONET/SDH, OTN, etc.).
Requirements for bandwidth management within a server layer
network are outside the scope of this document.
32 In an environment where an MPLS-TP layer network is supporting a
client layer network, and the MPLS-TP layer network is supported
by a server layer network then operation of the MPLS-TP layer
network MUST be possible without any dependencies on the server
or client layer network.
A. The server layer MUST guarantee that the traffic loading
imposed by other clients does not cause the transport service
provided to the MPLS-TP layer to fall below the agreed level.
Mechanisms to achieve this are outside the scope of these
requirements.
B. It MUST be possible to isolate the control and management
planes of the MPLS-TP layer network from the control and
management planes of the client and server layer networks.
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33 A solution MUST be provided to support the transport of a client
MPLS or MPLS-TP layer network over a server MPLS or MPLS-TP layer
network.
A. The level of co-ordination required between the client and
server MPLS(-TP) layer networks MUST be minimized (preferably
no co-ordination will be required).
B. The MPLS(-TP) server layer network MUST be capable of
transporting the complete set of packets generated by the
client MPLS(-TP) layer network, which may contain packets
that are not MPLS packets (e.g. IP or CNLS packets used by
the control/management plane of the client MPLS(-TP) layer
network).
34 It MUST be possible to operate the layers of a multi-layer
network that includes an MPLS-TP layer autonomously.
The above are not only technology requirements, but also operational
requirements. Different administrative groups may be responsible for
the same layer network or different layer networks.
35 It MUST be possible to hide MPLS-TP layer network addressing and
other information (e.g. topology) from client layer networks.
However, it SHOULD be possible, at the option of the operator, to
leak a limited amount of summarized information (such as SRLGs or
reachability) between layers.
2.3. Data plane requirements
36 It MUST be possible to operate and configure the MPLS-TP data
plane without any IP forwarding capability in the MPLS-TP data
plane. i.e. the data plane only operates on the MPLS label.
37 It MUST be possible for the end points of an MPLS-TP transport
path that is carrying an aggregate of client transport paths to
be able to decompose the aggregate transport path into its
component client transport paths.
38 A transport path on a link MUST be uniquely identifiable by a
single label on that link.
39 A transport path's source MUST be identifiable at its destination
within its layer network.
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40 MPLS-TP MUST be capable of using P2MP server (sub-)layer
capabilities as well as P2P server (sub-)layer capabilities when
supporting P2MP MPLS-TP transport paths.
41 MPLS-TP MUST be extensible in order to accommodate new types of
client layer networks and services.
42 MPLS-TP SHOULD support mechanisms to enable the reserved
bandwidth associated with a transport path to be increased
without impacting the existing traffic on that transport path
provided enough resources are available.
43 MPLS-TP SHOULD support mechanisms to enable the reserved
bandwidth of a transport path to be decreased without impacting
the existing traffic on that transport path, provided that the
level of existing traffic is smaller than the reserved bandwidth
following the decrease.
44 MPLS-TP MUST support mechanisms which ensure the integrity of the
transported customer's service traffic as required by its
associated SLA. Loss of integrity may be defined as packet
corruption, re-ordering or loss during normal network conditions.
45 MPLS-TP MUST support mechanisms to detect when loss of integrity
of the transported customer's service traffic has occurred.
46 MPLS-TP MUST support an unambiguous and reliable means of
distinguishing users' (client) packets from MPLS-TP control
packets (e.g. control plane, management plane, OAM and protection
switching packets).
2.4. Control plane requirements
This section defines the requirements that apply to an MPLS-TP
control plane. Note that it MUST be possible to operate an MPLS-TP
network without using a control plane.
The ITU-T has defined an architecture for Automatically Switched
Optical Networks (ASON) in G.8080 [ITU.G8080.2006] and G.8080 Amd1
[ITU.G8080.2008]. The control plane for MPLS-TP MUST fit within the
ASON architecture.
An interpretation of the ASON signaling and routing requirements in
the context of GMPLS can be found in [RFC4139] and [RFC4258].
Additionally:
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47 The MPLS-TP control plane MUST support control plane topology and
data plane topology independence. As a consequence a failure of
the control plane does not imply that there has also been a
failure of the data plane.
48 The MPLS-TP control plane MUST be able to be operated independent
of any particular client or server layer control plane.
49 MPLS-TP SHOULD define a solution to support an integrated control
plane encompassing MPLS-TP together with its server and client
layer networks when these layer networks belong to the same
administrative domain.
50 The MPLS-TP control plane MUST support establishing all the
connectivity patterns defined for the MPLS-TP data plane (i.e.,
unidirectional P2P, associated bidirectional P2P, co-routed
bidirectional P2P, unidirectional P2MP) including configuration
of protection functions and any associated maintenance functions.
51 The MPLS-TP control plane MUST support the configuration and
modification of OAM maintenance points as well as the activation/
deactivation of OAM when the transport path or transport service
is established or modified.
52 An MPLS-TP control plane MUST support operation of the recovery
functions described in Section 2.8.
53 An MPLS-TP control plane MUST scale gracefully to support a large
number of transport paths, nodes and links.
54 If a control plane is used for MPLS-TP, following a control plane
failure, the control plane MUST be capable of restarting and
relearning its previous state without impacting forwarding.
55 An MPLS-TP control plane MUST provide a mechanism for dynamic
ownership transfer of the control of MPLS-TP transport paths from
the management plane to the control plane and vice versa. The
number of reconfigurations required in the data plane MUST be
minimized (preferably no data plane reconfiguration will be
required).
2.5. Recovery requirements
Network survivability plays a critical role in the delivery of
reliable services. Network availability is a significant contributor
to revenue and profit. Service guarantees in the form of SLAs
require a resilient network that rapidly detects facility or node
failures and restores network operation in accordance with the terms
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of the SLA.
56 MPLS-TP MUST provide protection and restoration mechanisms.
A. MPLS-TP recovery techniques SHOULD be identical (or as
similar as possible) to those already used in existing
transport networks to simplify implementation and operations.
However, this MUST NOT override any other requirement.
B. Recovery techniques used for P2P and P2MP SHOULD be identical
to simplify implementation and operation. However, this MUST
NOT override any other requirement.
57 MPLS-TP recovery mechanisms MUST be applicable at various levels
throughout the network including support for link, transport
path, segment, concatenated segment and end to end recovery.
58 MPLS-TP recovery paths MUST meet the SLA protection objectives of
the service.
A. MPLS-TP MUST provide mechanisms to guarantee 50ms recovery
times from the moment of fault detection in networks with
spans less than 1200 km.
B. For protection it MUST be possible to require protection of
100% of the traffic on the protected path.
C. Recovery MUST meet SLA requirements over multiple domains.
59 Recovery objectives SHOULD be configurable per transport path.
60 The recovery mechanisms SHOULD be applicable to any topology.
61 The recovery mechanisms MUST support the means to operate in
synergy with (including coordination of timing) the recovery
mechanisms present in any client or server transport networks
(for example, Ethernet, SDH, OTN, WDM) to avoid race conditions
between the layers.
62 MPLS-TP recovery and reversion mechanisms MUST prevent frequent
operation of recovery in the event of an intermittent defect.
2.5.1. Data plane behavior requirements
General protection and survivability requirements are expressed in
terms of the behavior in the data plane.
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Note: Only nodes that are aware of the pairing relationship between
the forward and backward directions of an associated bidirectional
transport path can be used as end points to protect all or part of
that transport path.
63 It MUST be possible to provide protection for the MPLS-TP data
plane without any IP forwarding capability in the MPLS-TP data
plane. i.e. the data plane only operates on the MPLS label.
64 MPLS-TP protection mechanisms MUST support revertive and non-
revertive behavior.
65 MPLS-TP MUST support 1+1 protection.
A. Bidirectional 1+1 protection for P2P connectivity MUST be
supported.
B. Unidirectional 1+1 protection for P2P connectivity MUST be
supported.
C. Unidirectional 1+1 protection for P2MP connectivity MUST be
supported.
66 MPLS-TP MUST support the ability to share protection resources
amongst a number of transport paths.
67 MPLS-TP MUST support 1:n protection (including 1:1 protection).
A. Bidirectional 1:n protection for P2P connectivity MUST be
supported, and SHOULD be the default behavior for 1:n
protection.
B. Unidirectional 1:n protection for P2MP connectivity MUST be
supported.
C. Unidirectional 1:n protection for P2P connectivity is not
required and MAY be omitted from the MPLS-TP specifications.
D. The action of protection switching MUST NOT cause the user
data to enter an uncontrolled loop. The protection switching
system MAY cause traffic to pass over a given link more than
once, but it must do so in a controlled way such that
uncontrolled loops do not form.
Note: Support for extra traffic (as defined in [RFC4427]) is not
required in MPLS-TP and MAY be omitted from the MPLS-TP
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specifications.
2.5.1.2. Sharing of protection resources
68 MPLS-TP SHOULD support 1:n (including 1:1) shared mesh recovery.
69 MPLS-TP MUST support sharing of protection resources such that
protection paths that are known not to be required concurrently
can share the same resources.
2.5.2. Restoration
70 The restoration transport path MUST be able to share resources
with the transport path being replaced (sometimes known as soft
rerouting).
71 Restoration priority MUST be supported so that an implementation
can determine the order in which transport paths should be
restored (to minimize service restoration time as well as to gain
access to available spare capacity on the best paths).
72 Preemption priority MUST be supported to allow restoration to
displace other transport paths in the event of resource
constraint.
73 MPLS-TP restoration mechanisms MUST support revertive and non-
revertive behavior.
2.5.3. Triggers for protection, restoration, and reversion
Recovery actions may be triggered from different places as follows:
74 MPLS-TP MUST support fault indication triggers from lower layers.
This includes faults detected and reported by lower layer
protocols, and faults reported directly by the physical medium
(for example, loss of light).
75 MPLS-TP MUST support OAM-based triggers.
76 MPLS-TP MUST support management plane triggers (e.g., forced
switch, etc.).
77 There MUST be a mechanism to allow administrative recovery
actions to be distinguished from recovery actions initiated by
other triggers.
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78 Where a control plane is present, MPLS-TP SHOULD support control
plane restoration triggers.
79 MPLS-TP protection mechanisms MUST support priority logic to
negotiate and accommodate coexisting requests (i.e., multiple
requests) for protection switching (e.g., administrative requests
and requests due to link/node failures).
2.5.4. Management plane operation of protection and restoration
All functions described here are for control by the operator.
80 It MUST be possible to configure protection paths and protection-
to-working path relationships (sometimes known as protection
groups).
81 There MUST be support for pre-calculation of recovery paths.
82 There MUST be support for pre-provisioning of recovery paths.
83 The external controls as defined in [RFC4427] MUST be supported.
A. External controls overruled by higher priority requests
(e.g., administrative requests and requests due to link/node
failures) or unable to be signaled to the remote end (e.g.
because of a protection state coordination fail) MUST be
dropped.
84 It MUST be possible to test and validate any protection/
restoration mechanisms and protocols:
A. Including the integrity of the protection/recovery transport
path.
B. Without triggering the actual protection/restoration.
C. While the working path is in service.
D. While the working path is out of service.
85 Restoration resources MAY be pre-planned and selected a priori,
or computed after failure occurrence.
86 When preemption is supported for restoration purposes, it MUST be
possible for the operator to configure it.
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87 The management plane MUST provide indications of protection
events and triggers.
88 The management plane MUST allow the current protection status of
all transport paths to be determined.
2.5.5. Control plane and in-band OAM operation of recovery
89 The MPLS-TP control plane (which is not mandatory in an MPLS-TP
implementation) MUST be capable of supporting:
A. establishment and maintenance of all recovery entities and
functions
B. signaling of administrative control
C. protection state coordination (PSC). Since control plane
network topology is independent from the data plane network
topology, the PSC supported by the MPLS-TP control plane MAY
run on resources different than the data plane resources
handled within the recovery mechanism (e.g. backup).
90 In-band OAM MUST be capable of supporting:
A. signaling of administrative control
B. protection state coordination (PSC). Since in-band OAM tools
share the data plane with the carried transport service, in
order to optimize the usage of network resources, the PSC
supported by in-band OAM MUST run on protection resources.
2.5.6. Topology-specific recovery mechanisms
91 MPLS-TP MAY support recovery mechanisms that are optimized for
specific network topologies. These mechanisms MUST be
interoperable with the mechanisms defined for arbitrary topology
(mesh) networks to enable protection of end-to-end transport
paths.
2.5.6.1. Ring protection
Several service providers have expressed a high level of interest in
operating MPLS-TP in ring topologies and require a high level of
survivability function in these topologies. The requirements listed
below have been collected from these service providers and from the
ITU-T.
The main objective in considering a specific topology (such as a
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ring) is to determine whether it is possible to optimize any
mechanisms such that the performance of those mechanisms within the
topology is significantly better than the performance of the generic
mechanisms in the same topology. The benefits of such optimizations
are traded against the costs of developing, implementing, deploying,
and operating the additional optimized mechanisms noting that the
generic mechanisms MUST continue to be supported.
Within the context of recovery in MPLS-TP networks, the optimization
criteria considered in ring topologies are as follows:
a. Minimize the number of OAM entities that are needed to trigger
the recovery operation - less than are required by other recovery
mechanisms.
b. Minimize the number of elements of recovery in the ring - less
than are required by other recovery mechanisms.
c. Minimize the number of labels required for the protection paths
across the ring - less than are required by other recovery
mechanisms.
d. Minimize the amount of control and management plane transactions
during a maintenance operation (e.g., ring upgrade) - less than
are required by other recovery mechanisms.
e. When a control plane is supported, minimize the impact on
signaling and routing information exchange during protection -
less than are required by other recovery mechanisms.
It may be observed that the requirements in Section 2.5.6.1 are fully
compatible with the generic requirements expressed in Section 2.5
through Section 2.5.6 inclusive, and that no requirements that are
specific to ring topologies have been identified.
92 MPLS-TP MUST include recovery mechanisms that operate in any
single ring supported in MPLS-TP, and continue to operate within
the single rings even when the rings are interconnected.
93 When a network is constructed from interconnected rings, MPLS-TP
MUST support recovery mechanisms that protect user data that
traverses more than one ring. This includes the possibility of
failure of the ring-interconnect nodes and links.
94 MPLS-TP recovery in a ring MUST protect unidirectional and
bidirectional P2P transport paths.
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95 MPLS-TP recovery in a ring MUST protect unidirectional P2MP
transport paths.
96 MPLS-TP 1+1 and 1:1 protection in a ring MUST support switching
time within 50 ms from the moment of fault detection in a
network with a 16 nodes ring with less than 1200 km of fiber.
97 The protection switching time in a ring MUST be independent of
the number of LSPs crossing the ring.
98 The configuration and operation of recovery mechanisms in a ring
MUST scale well with:
A. the number of transport paths (must be better than linear
scaling)
B. the number of nodes on the ring (must be at least as good as
linear scaling)
C. the number of ring interconnects (must be at least as good
as linear scaling)
99 Recovery techniques used in a ring MUST NOT prevent the ring
from being connected to a general MPLS-TP network in any
arbitrary way, and MUST NOT prevent the operation of recovery
techniques in the rest of the network.
100 Recovery techniques in a ring SHOULD be identical (or as similar
as possible) to those in general transport networks to simplify
implementation and operations. However, this MUST NOT override
any other requirement.
101 Recovery techniques in logical and physical rings SHOULD be
identical to simplify implementation and operation. However,
this MUST NOT override any other requirement.
102 The default recovery scheme in a ring MUST be bidirectional
recovery in order to simplify the recovery operation.
103 The recovery mechanism in a ring MUST support revertive
switching, which MUST be the default behavior. This allows
optimization of the use of the ring resources, and restores the
preferred quality conditions for normal traffic (e.g., delay)
when the recovery mechanism is no longer needed.
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104 The recovery mechanisms in a ring MUST support ways to allow
administrative protection switching, to be distinguished from
protection switching initiated by other triggers.
105 It MUST be possible to lockout (disable) protection mechanisms
on selected links (spans) in a ring (depending on operator's
need). This may require lockout mechanisms to be applied to
intermediate nodes within a transport path.
106 MPLS-TP recovery mechanisms in a ring:
A. MUST include a mechanism to allow an implementation to
handle (including the coordination of) coexisting requests
or triggers (i.e., multiple requests - not necessarily
arriving simultaneously and located anywhere in the ring)
for protection switching based on priority. Note that such
coordination is the ring equivalent of the definition of
shared protection groups.
B. SHOULD protect against multiple failures
107 MPLS-TP recovery and reversion mechanisms in a ring MUST offer a
way to prevent frequent operation of recovery in the event of an
intermittent defect.
108 MPLS-TP MUST support the sharing of protection bandwidth in a
ring by allowing best effort traffic.
109 MPLS-TP MUST support sharing of ring protection resources such
that protection paths that are known not to be required
concurrently can share the same resources.
2.6. QoS requirements
Carriers require advanced traffic management capabilities to enforce
and guarantee the QoS parameters of customers' SLAs.
Quality of service mechanisms are REQUIRED in an MPLS-TP network to
ensure:
110 Support for differentiated services and different traffic types
with traffic class separation associated with different traffic.
111 Enabling the provisioning and the guarantee of Service Level
Specifications (SLS), with support for hard and relative end-to-
end bandwidth guaranteed.
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112 Support of services, which are sensitive to jitter and delay.
113 Guarantee of fair access, within a particular class, to shared
resources.
114 Guaranteed resources for in-band control and management plane
traffic regardless of the amount of data plane traffic.
115 Carriers are provided with the capability to efficiently support
service demands over the MPLS-TP network. This MUST include
support for a flexible bandwidth allocation scheme.
3. Requirements Discussed in Other Documents3.1. Network Management requirements
For requirements related to network management functionality
(Management Plane in ITU-T terminology) for MPLS-TP, see the MPLS-TP
Network Management requirements document [I-D.ietf-mpls-tp-nm-req].
3.2. Operation, Administration and Maintenance (OAM) requirements
For requirements related to OAM functionality for MPLS-TP, see the
MPLS-TP OAM requirements document
[I-D.ietf-mpls-tp-oam-requirements].
3.3. Network performance monitoring requirements
For requirements related to performance monitoring functionality for
MPLS-TP, see the MPLS-TP OAM requirements document
[I-D.ietf-mpls-tp-oam-requirements].
3.4. Security requirements
For a description of the security threats relevant in the context of
MPLS and GMPLS and the defensive techniques to combat those threats
see the Security Framework for MPLS & GMPLS Networks
[I-D.ietf-mpls-mpls-and-gmpls-security-framework].
For a description of additional security threats relevant in the
context of MPLS-TP and the defensive techniques to combat those
threats see the Security Framework for MPLS-TP
[I-D.ietf-fang-mpls-tp-security-framework].
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